The present invention relates to a gas turbine power plant, and more particularly, the present invention relates to a state-of-the-art gas turbine plant which is powered by a mixture of gases and steam.
The engines or devices that convert heat energy to mechanical energy are well known. Each of these engines belongs to one of four basic categories and have different heat energy cycles and efficiencies. Basically, those heat energy cycles and theoretical efficiencies are referred to as the Otto, Diesel, Brayton, and Rankine. Of these four cycles, the present invention is directed to those heat engines utilizing the Rankine cycle and those utilizing the Brayton cycle.
The Brayton heat engine cycle applies to a gas turbine engine which utilizes a heated gas driven power generating turbine while the Rankine cycle utilizes a steam driven turbine engine.
Each type of turbine engine has its own advantages. The gas turbine in its simplest application normally reaches about up to 30 percent efficiency, and is relatively light in weight for the amount of horsepower a particular unit can develop. The power-plant developing turbine normally runs at temperatures up to 2100.degree. F. and at entering gas pressures up to 10-12 atmospheres using selected clean, non-corrosive fuels such as petroleum or natural gas. The steam driven power-plant developing turbine generally runs at temperatures of about 1000.degree. F., limited by the steam boiler capability but utilizes pressures up to hundreds of atmospheres. Both high temperatures and high pressures increase power developing capability in a turbine. Each has found its use in industry and particularly in power plants.
There was a considerable amount of early work of attempting to devise a heat engine that would use steam and gases and would combine the benefits of both types of engines, steam and gas driven turbines. For early work in this area see, for instance, U.S. Pat. No. 708,027, U.S. Pat. No. 583,240, and the like.
Recently and especially in view of the oil embargoes, there has been a drive to utilize indigenous fuels and particularly solid fossil fuels and other solid fuels of which there is a great abundance in the United States rather than petroleum or natural gas fuels. When solid fuels are used in a gas turbine, they must be gasified, liquidified, or burned in solid form in a direct air suspension and cleaned if the combustion products are to be passed directly through the turbine. Alternatively, the solid fuels can be burned in an external combustion chamber utilizing heat exchangers to transfer thermal energy to drive the gas turbines. One effort in this area was that of Willyoung, U.S. Pat. No. 4,116,005. This patent discloses the utilization of a carbonaceous fuel powered gas turbine. A carbonaceous fuel such as, for instance, a slurry of coal, could be combusted to heat a compressed stream of air through a heat exchanger to a temperature in the range of 1200.degree.-1500.degree. F. and which would then be used to drive a gas turbine. The same heat exchanger-combustor was also used to turn water into steam which could be utilized to drive a steam turbine. The dual gas turbine-steam turbine was utilized in this system so as to increase the overall efficiency of the conversion of the heat energy available from one of the carbonaceous fuels. It is desirable to obtain additional power from the gas turbine in this system since the air that is utilized to drive the gas turbine can only be heated to a maximum temperature of up to 1500.degree. F. as a result of the corrosion tolerance of the metals utilized in such state-of-the-art heat exchangers even though most gas turbines are made of metals and also utilize blade cooling devices so that they can use non-corroding clean gases at temperatures of up to 1800.degree.-2100.degree. F.
It must also be appreciated that indirect heating of the air stream was used to drive the gas turbine since the direct combustion gases from the carbonaceous fuel could not be utilized directly to drive the gas turbine. Such Combustion gases could not be used to directly drive the gas turbine since they would corrode and degrade the metal of the gas turbine. Accordingly, an indirectly heated, compressed air stream which was heated in a heat exchanger by burning a carbonaceous fuel was utilized.
Further, due to the temperature tolerance of the state-of-the-art heat exchanger and as a result, of the limited temperature to which the gas stream was heated, the gas turbine engine alone could reach less than 20 percent efficiency. For the overall plant. however, the efficiency was increased by using the same heat exchanger apparatus to provide steam to drive a steam turbine and also by taking spent gases--particularly spent air--from the gas turbine and utilizing it regeneratively to burn the fuel in the combined combustor heat exchanger.
A different variation of such a dual use of gas turbine and steam turbine powered by the burning of carbonaceous fuels wherein the carbonaceous waste gases after being cooled were utilized to drive a second gas turbine, is disclosed in Willyoung, U.S. Pat. No. 4,223,529. However, this disclosure still does not show a gas turbine which is operated at the present state-of-the-art maximum temperature or efficiency because it again is powered by air heated indirectly through a heat exchanger by the burning of a carbonaceous fuel. There is also Kydd et al., U.S. Pat. No. 3,693,347 which discloses the use of a controlling means to optimize the injection of steam into combusted gases to drive a gas turbine. The gas turbine of this patent was not operated by the utilization of indirectly heated gases to drive the turbine; instead the gas turbine was driven directly by a mixture of combustion gases, and steam passing through the power generating turbine. It is important to note in this disclosure, and particularly Column 2 of the patent, the problems associated in the past with the use of steam injection in such gas turbines and how the inventor controls such problems or minimizes such problems as the result of his control over the steam injection rate.
Another method that was utilized to increase the efficiency of a gas turbine system operated by indirectly heated compressed gaseous streams through a heat exchanger by the burning of carbonaceous fuels, is to take the compressed gases after they had passed through the heat exchanger and add to them a clean hydrocarbon fuel and combust the mixture so as to increase the temperature level of the gaseous combustion product stream to 1800.degree.-2100.degree. F. and then use this combusted gas mixture to drive the gas turbine; see Willyoung, U.S. Pat. No. 4,253,300. By utilizing this method, there was able to be achieved an efficiency in the gas turbine engine alone of about 30 percent. However, the disadvantage of such a system was that it did not draw all its energy from the burning of the carbonaceous fuels and required additional expenditures for clean hydrocarbon fuel.
Accordingly, it was highly desirable to increase the efficiency of a commercially established state-of-the-art gas turbine which was powered by air or gases heated by indirect means. This is particularly true when the temperature capability of the gas turbine is considerably higher than that for the heat exchanger, which isolates the gas turbine from potentially destructive stream combusted gases forcing a derating of gas turbine inlet temperatures, rating and efficiency. Another heat engine that utilized both steam and a combusted gas is disclosed in Cheng, U.S. Pat. No. 3,978,661. However, the heat engine, or in one aspect the turbine, of U.S. Pat. No. 3,978,661, is driven or powered by both steam and clean combusted gases and had to be specially designed and built to meet those specifications. U.S. Pat. No. 3,978,661 nowhere discloses the use of a state-of-the-art gas turbine which could be operated by a combination of indirectly heated gases and steam such that the engine or the turbine could reach an efficiency of about 30 percent or the same value it would theoretically achieve if solid fuels could be fired directly.
Accordingly, it is one object of the present invention to disclose an improved power plant which utilizes a state-of-the art and commercially available gas turbine operated at derated turbine inlet temperature conditions which is powered by a combination of indirectly heated steam and gases.
It is an additional object of the present invention to disclose an improved power plant utilizing a state-of-the-art gas turbine which is powered, in part, by a gaseous stream heated indirectly by the burning of a carbonaceous fuel--such as, for instance, a coal slurry.
It is still an additional object of the present invention to provide an improved power plant in which there is a state-of-the-art gas turbine which is powered by both steam and an indirectly heated gas stream, both of which are heated and formed by passing them through a heat exchanger, and by the burning of a carbonaceous fuel.
It is yet an additional object of the present invention to provide an improved power plant having therein a state-of-the-art gas turbine powered by both gases and steam which are indirectly heated by the burning of wood or other biomass fuels.
It is a further object of the present invention to provide an improved power plant in which a state-of-the-art gas turbine is powered by gases and steam indirectly heated by the burning of a fossil fuel which gives off corrosive gases, and in which the gas turbine reaches an efficiency in the neighborhood of the value it would theoretically achieve when fired directly.
It is still a further object to the present invention to provide a process for operating an improved power plant having therein a commercial state-of-the-art gas turbine which is powered by an indirectly heated mixture of steam and gases such as air, and which gas turbine plant reaches an efficiency of about the same value it would theoretically achieve if the same fuel could be fired directly.